The roles of insulin and adrenal glucocorticoids in the control of the degradation of the muscle proteins actin and myosin are being studied. Techniques of measuring 3-Methyl histidine (3MH), a non- reutilizable amino acid component of actin and myosin have been developed. In vivo control experiments with normal rats have been performed where 3MH has been labeled and the loss of this compound from muscle followed. Experiments to determine the effects of insulin and adrenal glucocorticoids on the loss of 3MH from muscle are in progress. Measurements of the efflux of 3MH from muscle offers a unique opportunity to observe the effects of these hormones on the process of protein degradation without the inherent problems of amino acid uptake, amino acid recycling, and protein synthesis. These experiments have a direct bearing on the understanding of an important aspect of diabetes, namely, the role of hormones in controlling the increased degradation of muscle protein associated with chronic diabetes in man and other animals.